# Model Access Gateway – GPT-5.5 Chat Completions (x402)

> Model Access Gateway – GPT-5.5 Chat Completions (x402) is a paid API for AI agents from agent402-arb.rosariovitale0096.workers.dev, paid per call via x402, $0.0014/call, status unknown (last checked 2026-10-15).

Sends a chat completion request to GPT-5.5 via an OpenAI-compatible API, billed per-request in USDC on Base using x402 — no account or API key required.

## Facts

- Endpoint: POST https://agent402-arb.rosariovitale0096.workers.dev/llm/gpt-5.5?utm_source=zero.xyz
- Price: $0.0014/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/model-access-gateway-gpt-5-5-chat-completions-x402-eac47acc
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_eC0MEtO99WwdciXWvJR20

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability model-access-gateway-gpt-5-5-chat-completions-x402-eac47acc -d '<json body>'
```

Example prompt: Ask GPT-5.5 to write me a concise executive summary of the following meeting transcript — pay for it per-request in USDC using the x402 gateway so I don't need to set up an OpenAI account.

## When to prefer this

Choose this endpoint when you need GPT-5.5 chat completions without managing an OpenAI API key or subscription, and your agent or application can pay per-request in USDC via the x402 protocol on Base. Ideal for autonomous agents, Web3-native apps, or serverless pipelines where credential management is undesirable.

## Known failure modes

- Insufficient USDC balance — x402 payment fails, request rejected with 402 Payment Required
- Invalid or malformed message body — returns 400 with schema validation error
- Model unavailable or overloaded — returns 503 or timeout
- Network failure to the Cloudflare Worker — connection timeout or 5xx
- Token limit exceeded for the selected model — returns 400 or truncated response

## How this service works

GPT-5.5 API (openai/gpt-5.5): LLM inference via OpenAI-compatible chat completions, pay per call in USDC on Base with x402. No API key, no account. Suited for AI agents and scripts that need GPT-5.5 on demand. When listed, this request cost 30% less than the same request on BlockRun. Streaming and function calling supported. Exact price in the 402 quote before payment; automatic refund if the model fails to answer.

## Output

Returns an OpenAI-compatible chat.completion JSON object containing the assistant's message content, token usage breakdown (prompt, completion, total), finish reason, model identifier, and a completion ID.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "type": "string",
   "description": "Optional: fixed by the route (openai/gpt-5.5)"
  },
  "tools": {
   "type": "array"
  },
  "stream": {
   "type": "boolean",
   "description": "true: server-sent events after payment"
  },
  "messages": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "role"
    ],
    "properties": {
     "role": {
      "enum": [
       "system",
       "user",
       "assistant",
       "tool",
       "developer"
      ],
      "type": "string"
     },
     "content": {
      "type": [
       "string",
       "array",
       "null"
      ]
     }
    }
   },
   "minItems": 1
  },
  "max_tokens": {
   "type": "integer",
   "maximum": 16384,
   "minimum": 1,
   "description": "Optional, default 4096"
  },
  "temperature": {
   "type": "number",
   "maximum": 2,
   "minimum": 0
  },
  "response_format": {
   "type": "object"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "id": "chatcmpl-7f3c2a91",
  "model": "openai/gpt-5.5",
  "usage": {
   "total_tokens": 10,
   "prompt_tokens": 9,
   "completion_tokens": 1
  },
  "object": "chat.completion",
  "choices": [
   {
    "index": 0,
    "message": {
     "role": "assistant",
     "content": "OK"
    },
    "finish_reason": "stop"
   }
  ],
  "created": 1791979200
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/model-access-gateway-gpt-5-5-chat-completions-x402-eac47acc/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent402-arb.rosariovitale0096.workers.dev](https://www.zero.xyz/host/agent402-arb.rosariovitale0096.workers.dev/llms.txt)